Chemists redesign natural antifreeze

Chemists have created a family of synthetic compounds akin to proteins that keep

Natural antifreeze keeps the Antarctic mackerel icefish supple. K. Hoefling

Arctic and Antarctic fish from freezing stiff. If the new molecules can work as

well as the fish proteins do, they could offer a new route to protecting frozen

foods and chilled transplant organs from destructive ice buildup.

Researchers discovered these so-called antifreeze proteins in the 1960s (SN:

4/19/97, p. 237). Scientists believe that the compounds bind to tiny ice crystals

and make it harder for them to grow. Researchers have shown that the antifreeze

proteins can thwart ice-crystal formation when added to food.

Yet, researchers haven’t revealed molecular details of how the proteins work.

Also, harvesting the proteins from fish is costly and time-consuming, says chemist

Robert N. Ben of the State University of New York at Binghamton.

In the September-October Bioconjugate Chemistry, Ben and his colleagues report a

new method for chemically synthesizing molecules that resemble sugar-containing

antifreeze proteins called antifreeze glycoproteins.

The new chemical strategy creates a whole family of compounds, each one a

variation on natural antifreeze glycoproteins, the team reports. Structural

differences among the variants might help reveal the molecular motifs underlying

the natural antifreeze proteins. Also, the variants might be more or less suited

for specific anti-ice jobs, Ben says.

With an eye on commercial possibilities, the Binghamton team strengthened each of

its molecules by creating a strong carbon-carbon bond in the location where the

natural glycoproteins contain a weaker carbon-oxygen bond. With this added muscle,

the synthetic molecules remain intact under certain chemical and biological

conditions that destroy the natural glycoproteins, Ben says. That could make the

new chemicals promising for ice-thwarting coatings, additives, or sprays for

aircraft, concrete, or crops, he suggests.

Although the new molecules differ from the natural ones, Ben says preliminary

evidence suggests his compounds bind to ice and inhibit crystal growth.

Chi-Hing C. Cheng, a biologist at the University of Illinois at Urbana-Champaign,

calls the report “a gallant attempt” at synthesizing antifreezes. However, she

adds, Ben’s group must show that the molecules’ anti-ice powers rival those of the

natural glycoproteins or are better.

“Nature evolves a particular compound for a purpose,” Cheng says. The added

carbon-carbon bonds might make the new molecules more stable, but the proteins

might need the carbon-oxygen bonds for good antifreeze activity, she says.

If the new molecules do prove as effective as natural agents, then the new

synthesis techniques Ben’s team developed might suggest a route to commercially

viable antifreeze products, comments biochemist Robert E. Feeney of the University

of California, Davis. A specific application would be to prevent the buildup of

gritty ice granules in ice cream, he says.

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